Do you think my girlfriend is pregnant?

me and my girlfriend had unprotected sex twice in two days for not more then 10 secs. i didnt c*m inside her and i never came before. she should be getting her period anyday and has signs that she is going to get it (back pain, upset stomach etc.) but some of these are also signs of pregnancy...im just worried and i wanna know what you guys think... what are the chances that shes pregnant?